1. Field of the Invention
The present invention relates generally to an apparatus and method for performing Automatic Retransmission reQuest (ARQ) in a wireless communication system, and in particular, to an apparatus and method for performing ARQ in a multihop relay wireless communication system.
2. Description of the Related Art
Wireless data communications are subject to error depending on a channel condition of a radio resource interval. Error control and recovery technologies can be divided largely into Automatic Retransmission reQuest (ARQ) scheme and Frame Error Check (FEC) scheme. ARQ scheme requests retransmission of the errored data to a transmitter. FEC scheme corrects the error of corrupted data.
Particularly, in the ARQ scheme, error check result (e.g., Cyclic Redundancy Check (CRC)) has to be transmitted from a receiver to a transmitter. For instance, when the transmitter initially sends a packet, the receiver decodes the received packet. When the packet is not corrupted, the receiver sends Acknowledgment (ACK) signal to the transmitter. When the packet is corrupted, the receiver sends Negative Acknowledgement (NACK) signal to the transmitter.
Upon receiving the ACK signal, the transmitter sends a new packet. When receiving the NACK signal, the transmitter retransmits the previous packet.
In general, two retransmission schemes are utilized for stable data transfer in the wireless communication system. One is Media Access Control (MAC) ARQ in MAC layer, and the other is Hybrid ARQ (HARQ) in the physical (PHY) layer. In the following, the conventional MAC ARQ scheme is described.
FIG. 1 illustrates a conventional signal exchange procedure according to the ARQ scheme in a wireless communication system using an analog repeater (hereafter, referred to as a repeater).
The conventional wireless communication system includes one or more Base Stations (BSs), one or more repeaters, and one or more terminals. For a better understanding, BS 10, repeater 11, and terminal 12 are shown. It is assumed that two Protocol Data Units (PDUs) of the MAC layer are transmitted from BS 10 to terminal 12, and that terminal 12 receives data via repeater 11.
In FIG. 1, BS 10 generates one physical layer data (PHY DATA 1) with two MAC PDUs and sends it to repeater 11 in step 101. MAC PDU, which is the data transmission unit of the MAC layer, includes MAC header, payload containing real data, and an error check code (e.g., CRC code) for checking error of the payload. PHY DATA includes at least one MAC PDU.
Repeater 11 merely amplifies the amplitude of the PHY DATA 1 signal received from BS 10 and relays the amplified data to terminal 12 in step 103.
Terminal 12 decomposes the MAC PDUs in the PHY DATA 1 received from repeater 11 and checks error with respect to each MAC PDU in step 105. The error is checked using the error check code (CRC code) of the MAC PDU. Terminal 12 generates an error check code with the payload of the received MAC PDU and determines whether there exists error by comparing the generated error check code with the received error check code. In doing so, it is assumed that MAC PDU 2 among the decomposed MAC PDUs is corrupted.
When MAC PDU 1 is errorless and MAC PDU 2 is incorrect among the received data, terminal 12 sends a control message for responding to MAC PDU 1 with ACK and MAC PDU 2 with NACK to repeater 11 in step 107. Repeater 11 amplifies the signal amplitude of the control message received from terminal 12 and relays the amplified message to BS 10 in step 109.
BS 10 recognizes the retransmission-requested MAC PDU by analyzing the control message from repeater 11 in step 109. That is, BS 10 recognizes the retransmission request of MAC PDU 2. Accordingly, BS 10 generates PHY RETRANSMISSION DATA with the retransmission-requested MAC PDU 2 and sends it to repeater 11 in step 11. Repeater 11 amplifies the signal amplitude of PHY RETRANSMISSION DATA from BS 11 and relays the amplified data to terminal 12 in step 113. As such, terminal 12 requests the retransmission of the incorrect data to BS 11 via repeater 11 and receives the retransmission data via repeater 11.
As discussed above, the repeater in the wireless communication system functions to amplify and relay the analog signals transmitted and received between the BS and the terminal. However, since the repeater currently developed has both the MAC layer and the PHY layer, it can interpret messages transceived between the transmitter and receiver. Thus, the mere signal amplification and relay may be quite inefficient. Therefore, what is needed is an ARQ method using an improved repeater in the wireless communication system.